Self-similarity and scaling relations for microearthquakes at Mt. Etna volcano (Italy)

In this study, forty-eight Etnean microearthquakes, recorded with a local network of three seismic digital stations, have been analysed in order to infer source properties and scaling relations. Seismic moments, fault radii, stress drops and seismic energies have been determined from the SH displacement spectra using the source model of Brune (1970, 1971). The Equivalent Wood-Anderson magnitude (MWAeq) has been estimated for the whole data set. The relationship between log-stress drop and log-moment is linear up to a moment of 10(12) N m, whereas for higher moments the slope of the regression-straight line is not significantly different from zero. For moments less than 10(12) N m, there is no significant trend in the log-moment as a function of source radius, whereas for higher moments the log-moment increases with radius. The main conclusion is that the stress drop is the dominant scaling factor for moments less than 10(12) N m, against the self-similarity assumption (Aki, 1967): we hypothesize that such a deviation from self-similarity is related to a heterogeneous medium with barriers on the fault. On the contrary, for higher moments, the source dimension becomes the controlling factor and self-similarity holds. The relationships between log-energy and log-moment, MWAeq and log-moment, MWAeq and log-energy show a high degree of linear correlation. Finally, the whole data set is consistent with the Gutenberg-Richter magnitude-energy relation. (C) 1997 Elsevier Science B.V.